Researchers find wasp can strike down giant reed

Scientists have discovered a beneficial wasp in southern California that attacks a highly invasive weed, saving the federal government time and money that would have been spent to import the insect from Europe.

Once used to make reeds for woodwind musical instruments, a bamboo-like plant called giant reed or Arundo donax has pushed its way through the southwestern United States and Mexico.

Giant reed, originally brought to North America from the Mediterranean region, was used to control erosion, but the plant is a double-edged sword because it chokes riversides and stream channels, crowds out native plants, interferes with flood control and increases fire potential. Canes that are dislodged during high river flows pile up and form debris dams behind bridges, culverts and other structures.

Because giant reed grows and expands to large areas quickly, it can invade new areas, and, once established, it overpowers native vegetation. Wildlife loses out because Arundo is not useful for nesting or for providing food supplies that sustain native species.

"Land managers treat Arundo with herbicides and bulldoze river bottoms to reduce its abundance, but these control methods have their own adverse effects on sensitive riparian environments," says Tom Dudley, associate research biologist at the UC Santa Barbara Marine Science Institute. "The USDA has been looking for ways to suppress growth of Arundo to a level where its impacts are tolerable or below an ecological or economic threshold, and that would allow native vegetation to recover its dominance."

Two European beneficial insects that the USDA is working with are already here and could eventually provide natural control of the weed throughout the Southwest.

"We've confirmed that Tetramesa romana is genetically the same as wasps back in its native Mediterranean region, so the USDA won't have to import it to control giant reed," Dudley says.

Extensive surveys by postdoctoral researcher Adam Lambert also found that another candidate for importation, a "shootfly" of the genus Cryptonevra, is also here.

Tetramesa romana is currently in quarantine in Texas for biological control testing and development. In the meantime, Dudley and Lambert are studying the distribution and impact of the wasp on giant reed populations in Santa Barbara, Ventura, Los Angeles, Orange and San Diego counties. This information will be used to monitor the wasp's movement and establishment, as well as to study how Arundo and the environment respond to the wasps after they are released.

"We're determining how easily the wasp can be introduced elsewhere, starting with an introduction into northern Santa Barbara County," says Dudley. "The wasp readily infiltrates uninfested stands in garden plots, and we may be able to use it in other areas of the West that don't have the wasps.

"We're also comparing plant diversity, decomposition rates, soil moisture, and light availability in Arundo-infested and uninfested areas. Initial results show that giant reed negatively impacts all of these parameters. We're hopeful these insects will provide an ecologically benign solution to reducing the damage from this destructive weed."

The UC Exotic/Invasive Pests and Diseases Research Program funded this project.

The UC Exotic/Invasive Pests and Diseases Research Program targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is a collaboration between the UC Statewide Integrated Pest Management Program and the UC Riverside Center for Invasive Species Research. U.S. Department of Agriculture, Cooperative State Research Education and Extension Service, funds the program.